Tyneside is to bear the brunt of up to 300 job losses at National Grid, which is transferring work to India.
A total of 163 posts are to be lost at the energy firm's Newcastle office, which is to close. Another 137 jobs will go in Warwick and Northampton.
The company said those affected worked in its shared services division and carried out mainly finance and human resource roles.
Union leaders pledged to fight the planned job losses.
National Grid said all those facing redundancy would have the opportunity to apply for jobs elsewhere within the company.
National Grid is to transfer some of its work to Tata Consultancy Services, a company based in India, which already provides information systems.
In September workers on Tyneside took part in a 24-hour stoppage over plans to outsource work to India.
Gary Smith, GMB national secretary for energy, said "National Grid have been trying to deny for many months what they have confirmed today.
"GMB will not accept that this company which makes multi billions profits as a monopoly supplier has the right to export these jobs from UK at a time of very high unemployment across the land.
"We pledge to step up our fight to stop this national greed."
Mike Jeram, Unison's head of business and environment, added: "We are appalled that a company that makes a huge profit from UK customers and has just paid out the highest ever dividend to shareholders is prepared to sacrifice the staff who helped them do this."